1. Field of the Invention
The present invention relates to a duplicate synchronization system. In particular, the present invention relates to a duplicate synchronization system and a method of copying the contents of a memory in the duplicate synchronization system.
2. Description of the Related Art
A fault tolerant (FT) computer is known as a computer providing high reliability. In the FT computer, hardware modules constituting a system are duplicated or multiplexed, and these hardware modules are controlled so as to operate in synchronization with each other. A system such as the FT computer system is referred to as a “duplicate synchronization system” hereinafter. According to the duplicate synchronization system, even when a fault occurs in a certain section (module), it is possible to continue processing in a normal module by separating the fault module. That is to say, the duplicate synchronization system has excellent fault tolerance and availability (for example, refer to Japanese Laid Open Patent Application JP-P-Heisei 10-293697).
The duplicate synchronization system consists of a first system and a second system. In a normal operation, data stored in main memories of both systems are controlled to be always consistent with each other. On the other hand, at the time of system start-up or system restoration after system failure, data stored in the main memories of both systems are not consistent. It is therefore necessary to copy data stored in the main memory of one system to the main memory of the other system as soon as possible and thereby make the both system consistent with each other.
When the one system as a copy source is normally operated during a data restoration process, the data stored in the main memory of the one system is updated. It is therefore necessary to suspend the operation of the whole duplicate synchronization system during the data restoration process. Since the increase in the time for the data restoration disturbs the services, it is preferable that the suspended period is as short as possible. In particular, capacity of the main memory goes on increasing in recent years, and thus a time required for the data copy between the both systems becomes longer and longer. The time required for the data copy is referred to as a “memory copy time” hereinafter. In addition, transfer performance of a data link path connecting between the systems is lower as compared with data transfer performance in an LSI. This is also one of factors which cause the increase in the memory copy time. It is desired to reduce the memory copy time and to shorten the suspended period of the duplicate synchronization system.